Changes to error messages in Git 2.4.3 cause Stash to misinterpret them

Changes in git's error messages cause Stash to misinterpret certain errors from git, which may produce undesirable results.

Changes are caused by error message format changes in git's refs.c:

https://github.com/git/git/commit/faa4b2ecbb6ea5fdc8d685343c4985dfb97f4dbf#diff-e3d30a16dfc234b7f6c1129955f5c0ac

and mean instead of *RefNameException Stash's git code throws CommandFailedException.